Cystic fibrosis-related diabetes (CFRD) is commonly thought to be a consequence of insulin deficiency combined with insulin resistance. However, this explanation is not satisfactory because clinical studies in CFRD show inadequate insulin secretion but little evidence for insulin resistance. Furthermore, the commonly accepted pathogenesis for the insulin deficiency, namely that the pancreatitis of cystic fibrosis (CF) and subsequent pancreatic atrophy and fibrosis lead to islet destruction, is not likely a sufficient explanation. Since the cystic fibrosis transmembrane conductance regulator (CFTR) is expressed and functional in mouse and human pancreatic islet cells, we propose that CFTR mutations directly impair islet cell function and health. In this proposal, we will test the hypotheses that CFTR plays an important regulatory role in insulin and glucagon secretion and that mutations in CFTR lead to ? cell dysfunction, inadequate ? cell adaptation to islet stressors (pancreatitis, inflammation, hyperglycemia), and reduced ? cell mass, thus greatly increasing the risk for diabetes mellitus. We propose an integrated, multiple component pathogenesis involving abnormal CFTR ion channel activity and abnormal CFTR protein trafficking and cell biology, leading to secretory dysfunction, ? cell ER stress, and ? cell death. Our multidisciplinary team with expertise in electrophysiology, human islet biology, and CF will conduct in vitro and in vivo studies using unique mouse models and human islets to test these hypotheses and to discover information important for understanding the pathogenesis of human CFRD. We will pursue three aims: 1) Define the role of CFTR in regulating insulin and glucagon secretion and ? cell function and health by studying islets lacking CFTR; 2)Determine the impact of selected CF mutations on insulin and glucagon secretion and ? cell function and health; and 3) Determine the impact of selected CF mutations on ? cell function, health, and adaptation in response to islet stressors such as pancreatitis, hyperglycemia, and insulin resistance.